Electrochemical CO₂ reduction is a viable, economical, and sustainable method to transform atmospheric CO₂ into carbon-based fuels and effectively reduce climate change and the energy crisis. Constructing robust catalysts through interface engineering is significant for electrocatalytic CO₂ reduction (ECR) but remains a grand challenge. Herein, SnO₂/Bi₂O₂CO₃ heterojunction on N,S-codoped-carbon (SnO₂/BOC@NSC) with efficient ECR performance was firstly constructed by a facile synthetic strategy. When the SnO₂/BOC@NSC was utilized in ECR, it exhibits a large formic acid (HCOOH) partial current density (J_HCOOH) of 86.7 mA·cm⁻² at −1.2 V versus reversible hydrogen electrode (RHE) and maximum Faradaic efficiency (FE) of HCOOH (90.75% at −1.2 V versus RHE), respectively. Notably, the FE_HCOOH of SnO₂/BOC@NSC is higher than 90% in the flow cell and the J_HCOOH of SnO₂/BOC@NSC can achieve 200 mA·cm⁻² at −0.8 V versus RHE to meet the requirements of industrialization level. The comparative experimental analysis and in-situ X-ray absorption fine structure reveal that the excellent ECR performance can be ascribed to the synergistic effect of SnO₂/BOC heterojunction, which enhances the activation of CO₂ molecules and improves electron transfer. This work provides an efficient SnO₂-based heterojunction catalyst for effective formate production and offers a novel approach for the construction of new types of metal oxide heterostructures for other catalytic applications.